is a 10 degree drop in intake temp the same as a 10 degree drop in outside temp?

Discussion in 'PSI Superchargers Tech Questions' started by Will Hanna, Sep 6, 2008.

  1. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
    Staff Member

    Joined:
    May 6, 2003
    Messages:
    6,688
    Likes Received:
    125
    here's one for the resident experts.....

    let's say you get your psi blower coated by cantrell and achieve a 10-15 degree drop in intake temperature. would that drop in intake temperature have the same effect as the outside air dropping the same amount?

    i haven't monitored intake temperature in any of the cars i've worked with, i'm curious to the correlation between outside ambient temp and it's effects on intake temp. regardless of the coating or blower, how closely correlated is the outside temp to the intake temp? does 10 degrees change outside equal 10 degrees inside? 5 degrees inside? nil change??

    i realize i could very likely get little response on this because it may 'compromise sensitive information'....
     
    #1
  2. Ron C

    Ron C Jr. Dragster

    Joined:
    Mar 4, 2005
    Messages:
    519
    Likes Received:
    1
    Well, lets just look at it from a density factor and oxygen by volume in both cases without specific numbers. If the ambient air temp dropped 10 degrees and say that would be from 80 to 70 degrees the percentage density factor change would be significantly greater than changing from 260 to 250 degrees in oxygen per volume. Heated air is a lot thinner.
    Does that make sense?

    Blessings.........Ron Clevenger.
     
    #2
  3. Dave Germain

    Dave Germain New Member

    Joined:
    Aug 1, 2003
    Messages:
    896
    Likes Received:
    0
    Will, I took a wild guess and ran two sets of data on jetsize. Ten degrees difference in temps is approx. 700 feet difference in density altitude. I didn't run the full equation to see what 700 feet of elevation does to my main jet though. I would think a good comparison would be a before and after plug reading. Would the motor read leaner after the blower coating ? If so I would think that would be an awfully good reason for coating your blower.
    Dave Germain
     
    #3
  4. SoDak

    SoDak Active Member

    Joined:
    Dec 29, 2006
    Messages:
    1,524
    Likes Received:
    3
    I go 500 feet per MP size change.
     
    #4
  5. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
    Staff Member

    Joined:
    May 6, 2003
    Messages:
    6,688
    Likes Received:
    125
    screw vs. roots

    ron,

    i see what you're saying, but I don't think the screw blower puts out that hot of a charge.

    what you're saying is the cooler the temp range we're discussing, the bigger the gain.
     
    #5
  6. nitrohawk

    nitrohawk New Member

    Joined:
    Dec 28, 2003
    Messages:
    1,016
    Likes Received:
    0
    I have no experience with blown alcohol but plenty of experience with screw compressors. I can tell you that on this type application the discharge air temp goes up or down the same amount as ambient temp change.
     
    #6
  7. semi-automan

    semi-automan New Member

    Joined:
    Aug 24, 2003
    Messages:
    23
    Likes Received:
    0
    Pandora's box

    The oxygen content in the manifold is strictly the result of the air quality being drawn into the manifold ie. cooling the air in the manifold changes boost pressure not oxygen content. Since the blower air volume is controlled by its rpm. I would suggest hot air, friction, and lower hp loss from energy required to create less boost come into play here.
     
    #7
  8. Ron C

    Ron C Jr. Dragster

    Joined:
    Mar 4, 2005
    Messages:
    519
    Likes Received:
    1
    I just threw those intake air temps out there because that was what I was seeing on my blown gas nonintercooled deal with 108 degree ambients at Sacramento a few months ago.

    A good way to get ones brain around all this is, have you ever taken a plastic 5 gallon fuel jug with being half full of gas and had it setting the the Sun for awhile?
    It really swells up with pressure. The heat has caused the fuel to expand and the trapped air inside expand as well. Before you open the cap nothing has changed inside the fuel jug related to amount of total BTU's of energy in the fuel and the total amount of oxygen in the air. So we release the fuel jug cap and the expanded air equalizes itself with the ambient atmosphere and then tighten the cap again. Everything has changed inside the fuel jug except for the total BTU's of energy in the gas in the jug but the relationship to everything has changed. The fuel displaces a greater volume and the total oxygen contained in the displaced air (inside sealed jug again) is less.
    So if you are running this fuel through a fix'd jet and preset fuel pressures the cooler fuel that took up less room before it was heated will pass more total BTU's of potential energy than the expanded heated fuel.
    The same principal applies to the oxygen in the air. While the air was trapped in the heated fuel jug the total oxygen content remained the same. But once it was released (blower discharge) it will take up more space with less oxygen per volume.
    Hope this makes sense, internet discussions can be really hard to communicate ideas like these.

    Anyway, long way around in saying the same degree change in ambient vs blower discharge or port air temp would not produce the same amount of oxygen change.

    Blessings..........Ron Clevenger.
     
    #8
  9. nitrohawk

    nitrohawk New Member

    Joined:
    Dec 28, 2003
    Messages:
    1,016
    Likes Received:
    0
    Don't know how this thread got so far off base.
    I thought the question was if a 10 degree change in ambient temp would result in a 10 degree change in the air temp in the manifold
     
    #9
  10. TOL

    TOL Active Member

    Joined:
    May 18, 2005
    Messages:
    1,305
    Likes Received:
    16



    Hi Will. The question that you asked is a good one, but it does not have a straight forward answer. The best answer that I can suggest is that the correlation between ambient air temperature and measured intake manifold temperature will vary according to a whole host of factors, but, it should always be predictable for a given combination.

    The things which would affect this relationship would include the following: compressor adiabatic efficiency, compressor design, compressor type, fuel split between the hat & ports, type of fuel and fuel load, overdrive, intake manifold heat soak/absorption, method of measuring the intake charge temps (which is complicated by fuel wetting & vaporization), degree of fuel atomization, and…..well, you get the picture.

    However, if you want to narrow the scope down to just the before & after for a given screw compressor atop a given engine setup, then this is what the thermodynamic relationships dictate:

    For a screw compressor at say 70% adiabatic efficiency, the delta change in temperature from the hat to the manifold would be:

    T2=((T1*(P2/P1)^k )/(.7))-(Delta T fuel evap)

    T2 = manifold temp
    T1 = ambient temp
    P2 = manifold boost
    P1 = ambient pressure
    K = .28571 (for sake of argument)
    Delta T evap = cooling effect of meth (110 F for sake of argument)
    Temperature is F+460 (degrees F)
    Pressure is P+15 (psig)


    So if you were racing methanol on a 100F day, with 40 psig boost in the manifold, at an unchanging ambient baro & humidity, then the expected manifold temp might reasonably be ((((560*(55/15)^.28571)/(.7))-(570))-460 = about 130 degrees F give or take a few degrees for sake of example.

    If you were to drop the ambient temperature by 10 degrees F for the same setup and day, then the anticipated manifold temp might well reasonably be ((((550*(55/15)^.28571)/(.7))-(570))-460 = about 108 degrees F again for sake of example.

    In other words, a 10 degree drop in ambient temp “might” well show up as a 20 degree change in manifold temp for the same compressor atop the same engine with the same setup on the same day.

    In your example you cited a 10 degree temp drop in the intake manifold, but did not quote the corresponding change in measured intake manifold pressure, if any. If you know the before & after intake manifold pressures and temperatures then you can figure out the relative change of density of the intake manifold charge (change of oxygen content) and can then work that back through the formulas to figure out how much of a change of ambient temperature that represents, in order to use standard off-the-shelf tuning programs. Or, you could more easily just figure out the change in the relative manifold density, and work from that for the tuneup.

    The relative change of charge density within the manifold, before and after, can be calc’d as follows:

    New density/Old Density = (Pnew*Told)/(Pold*Tnew)

    Hope that helps? To model with any more accuracy would require a lot of messy thermo equations. Without a doubt the best way is to keep a log of ambient temps versus intake manifold temps, for your combination, or even better P & T for both the ambient and the manifold. Plug those numbers into an Exel spreadsheet, and then graph them, and there you will have a quick set of empirical and visual relationships for your exact combination.

    So I guess the short answer to your question is that the relationship between ambient air temp and manifold charge temp is highly dependant upon your exact setup. The change in manifold charge density, or fuel requirement, or change in power potential, can be estimated as described above (for methanol).
     
    #10
  11. Ron C

    Ron C Jr. Dragster

    Joined:
    Mar 4, 2005
    Messages:
    519
    Likes Received:
    1


    Unless I'm wrong I think he was wondering if the 10 degree drop in ambient has the same power potential as a 10 degree drop "after" the blower. If your just looking at oxygen I still say no per volume. The heated expanded air coming out of the blower will have less oxygen by volume.
    But when you add oxygenated fuels with high evap rates that would be part of the equation in the final tune up. And the overall influence does get complicated for combustion purposes when you have ambient latent heat (water) on one side and running it through the compressor which results in sensible heat (dry air) and combining the too. It's still calculable.

    Anyway it's fun to stretch the cobwebs in the brain.

    Blessings...........Ron.
     
    #11
  12. Lonnie Houde

    Lonnie Houde Member

    Joined:
    Nov 14, 2005
    Messages:
    252
    Likes Received:
    0
    I dont know about the power increase. But I have most of my customers monitor their blower outlet temps. On an 85 degree day Idle temp is usually just below ambient by 5-7 degrees. At the end of an eight mile run the manifold temps range from 145-150 degrees with 55lbs of boost. On a quater mile run. The temps are usually between 155-160 degrees, with 58-60lbs of boost. These are with C rotor blowers at 116-120% over. I am going to be doing some RnD on our dyno this winter with coatings and whatnot with some customers' screw blowers.
     
    #12

Share This Page